In U.S. Pat. No. 5,739,218, there is described what is believed to be the first family of radially layered poly(amidoamine-organosilicon) PAMAM.sub.x OS.sub.y dendrimers, which contain concentric layers, i.e., generations, of hydrophilic poly(amidoamine) PAMAM.sub.x branch cells in their interior, and hydrophobic organosilicon (OS) branch cells in their exterior. U.S. Pat. No. 5,739,218 also describes what is believed to be the first family of radially layered poly(propyleneimine-organosilicon) PPI.sub.m OS.sub.n dendrimers, which contain concentric layers of hydrophilic poly(propyleneimine) PPI branch cells in their interior, and hydrophobic organosilicon (OS) branch cells in their exterior.
While U.S. Pat. No. 5,739,218 specifically points out that the hydrophilic interior may constitute a generation 0 to a generation 10 poly(amidoamine) dendrimer, i.e., PAMAM.sub.x where x represents an integer from 0 to 10, or a generation 0 to a generation 5 poly(propyleneimine) dendrimer, i.e., PPI.sub.m where m represents an integer from 0 to 5, it does not specify the number of organosilicon layers or generations, i.e., y and n, respectively, in the respective dendrimer exteriors.
However, U.S. Pat. No. 5,739,218 does specify the particular organosilicon reagents, as well as the reactions, that are used in the preparation of the radially layered poly(amidoamine-organosilicon) PAMAM.sub.x OS.sub.y and poly(propyleneimine-organosilicon) PPI.sub.m OS.sub.n dendrimers; from which it can be deduced that the PAMAM.sub.x OS.sub.y and PPI.sub.m OS.sub.n dendrimers in U.S. Pat. No. 5,739,218, contain at least one but no more than two layers of OS.sub.y and OS.sub.n branch cells.
This follows from the fact that in U.S. Pat. No. 5,739,218, in reactions with the amine NH.sub.2 terminated PAMAM.sub.x or PPI.sub.m, OS.sub.y and OS.sub.n reagents such as (3-acryloxypropyl)methyldimethoxysilane, chloromethyltrimethylsilane, iodomethyltrimethylsilane, chloromethyldimethylvinylsilane, as well as (3-acryloxypropyl)bis(vinyldimethylsiloxy)methylsilane and (3-acryloxypropyl)tris(trimethylsiloxy)silane, are employed.
The first four of these reagents will necessarily provide PAMAM.sub.x OS.sub.y and PPI.sub.m OS.sub.n dendrimers with a single outermost layer of OS.sub.y and OS.sub.n branch cells, i.e., y and n=1, while the latter two reagents provide dendrimer homologues with at most two OS.sub.y and OS.sub.n branch layers in the exterior, i.e., y and n=2.
It should be noted that computer modeling studies have confirmed that experimentally observed dramatic changes in the solubility behavior of such dendrimers are the direct consequence of their degree of surface coverage by hydrophobic units such as trimethylsilyl, i.e., --Si(CH.sub.3).sub.3 units (TMS). Thus, it can be reasonably expected that further increases in dendrimer surface coverage by OS.sub.y and OS.sub.n branch cells would lead to further changes in this and other dendrimer properties.
For example, in addition to changes in solubility behavior, other properties which can be affected include surface characteristics, such as surface tension, contact angle, and phase transport behavior; as well as properties such as Theological flow behavior, glass temperature, thermal and thermo-oxidative degradation behavior, chemical reactivity, and electrical properties.
By way of illustration, a dramatic effect of the degree of substitution of --NH end groups of a PAMAM.sub.x precursor, by methylene trimethylsilyl units, i.e., --CH.sub.2 Si(CH.sub.3).sub.3, on the solubility of PAMAM.sub.x OS.sub.y dendrimers, has been confirmed. Thus, it was demonstrated that an increase in hydrophobicity of the dendrimer outer surface, i.e., an increase in the degree of substitution of --NH groups by TMS units, changed the ability of an unmodified PAMAM.sub.x dendrimer to dissolve in water and methanol, into a completely new composition dependent property.
For example, a 50 to 60 percent substituted homologue, i.e., a PAMAM.sub.x OS.sub.y dendrimer in which all end groups are at least secondary amine units, acquired the ability to dissolve in polar organic solvents such as chloroform and tetrahydrofuran (THF); the 68 percent substituted derivative lost the ability to dissolve in water; while the completely substituted dendrimer gained the completely new characteristic of being soluble in a hydrocarbon such as toluene.
Therefore, since the radially layered poly(amidoamine-organosilicon) PAMAM.sub.x OS.sub.y and the poly(propyleneimine-organosilicon) PPI.sub.m OS.sub.n dendrimers described in U.S. Pat. No. 5,739,218 contain only either one or two layers of the respective OS branch cells, i.e., y and n=1 or 2; and U.S. Pat. No. 5,739,218 would not enable one skilled in the art to obtain higher homologues thereof, i.e., PAMAM.sub.x OS.sub.y or PPI.sub.m OS.sub.n dendrimers containing at least three or more exterior layers of OS branch cells, i.e., y and n=3 or more; new methods of preparing such dendrimers were discovered in accordance with this invention.
Thus, in one embodiment of a method according to the invention, the method is based on a coupling reaction between a PAMAM.sub.x or a PPI.sub.m dendrimer with an independently prepared regular OS.sub.y or OS.sub.n dendron, or with a statistical OS.sub.y or OS.sub.n hyperbranched polymer. In resulting PAMAM.sub.x OS.sub.y or PPI.sub.m OS.sub.n dendrimer products according to this embodiment, the number of layers of OS.sub.y or OS.sub.n branches is regulated by the number of OS.sub.y or OS.sub.n branch cells in the OS.sub.y or OS.sub.n dendron or hyperbranched polymer used in the coupling reaction. In this regard, the products obtained from regular dendrons and statistical hyperbranched polymers are considered, for purposes herein, as being compositional analogues, which means that for the same composition, they differ only in the degree of their structural regularity.
In the other embodiment of this invention, the method is based on hydrosilation of a PAMAM.sub.x OS.sub.y or a PPI.sub.m OS.sub.n dendrimer of the type described in U.S. Pat. No. 5,739,218, containing vinyl or allyl groups as the end units. According to this alternate embodiment, it is possible to obtain PAMAM.sub.x OS.sub.y or PPI.sub.m OS.sub.n dendrimers in which y and n are three or more.
These two methods are believed to be new, and dendrimers containing OS.sub.y or OS.sub.n branches which are prepared according to these two new methods are also believed to be new. Dendrimers containing at least three or more OS.sub.y or OS.sub.n branches are believed to be new regardless of the method used in their preparation.